1. Field of the Invention
The present invention relates to a method of scanning in an optical device, and more particularly to such a method which is adapted to produce a high resolution image.
2. State of the Prior Art
Exposure systems for recording information on a light-sensitive recording medium often employ multiple radiation sources operating in parallel to decrease the aggregate amount of time required to complete the exposure. In U. S. Pat. No. 4,389,655, there is shown an optical device for non-impact recording in which a recording head includes a linear array of optical fibers. A recording medium is moved relative to the recording head, and the fibers of the head are arranged with their output ends extending in a direction transverse to the direction of movement of the recording medium. A light source is connected to each of the fibers at an input end, and each of the light sources is modulated in accordance with an information signal to produce a desired image. A problem with devices of the type shown in this patent is that it is often desirable to expose a line pattern having a spacing between lines (called the raster spacing) which is smaller than the closest possible spacing of the sources, the closest spacing being determined by the physical size of the sources.
Various methods have been used to decrease the raster spacing. One method has been to tilt the array of sources at an angle other than perpendicular to the direction of the lines, as shown, for example, in U. S. Pat. No. 4,435,064. Tilting of the array, however, requires the data in various lines to be delayed by differing amounts, and elongates the pattern of sources in the direction of the lines. Tilting of the array also causes any deviation of the sources from a straight line to be converted into unequal spacing of the exposed lines. Thus, other methods of decreasing the spacing have been tried including the interleaving of images, as shown, for example, in U. S. Pat. No. 4,198,158.
U. S. Pat. No. 4,198,158, discloses a method for superposing a plurality of matrix display images on a record medium. Successive images presented on a plasma panel are caused to be offset from one another on the record medium by interposing a tilted plate of glass between the plama panel and the record medium. One of the problems with this system is that matrix displays are not suitable for use in many types of recording apparatus, such as, for example, drum recorders. A further problem is that the size of the image which can be exposed is limited by the size of the display.